1. Field of the Invention
The present invention relates to oscillators and more particularly to negative resistance oscillators produced by connecting a parallel tuned resonant circuit to a two terminal negative resistance circuit. A negative resistance circuit is one in which an increase in voltage results in a decrease in current. More particularly, the negative resistance oscillator herein described employs a plurality of transistors connected to exhibit the foregoing negative resistance characteristics and is fabricated of components suitable for integration into a monolithic substrate.
2. Description of the Prior Art
Negative resistance oscillators are known per se and the individual circuits which comprise the oscillator include current sources and current sinks which are known per se. Such circuits are, for instance, described in a book entitled "Analogue Integrated Circuit Design" by Aaron B. Grebene, published in 1972 by Von Nostrand Reinholdt Company.
In integrated circuit application, a negative resistance oscillator must ordinarily satisfy a complex set of constraints consistent with the overall integration technique. More particularly, assuming that a particular circuit function is to be added to other IC circuitry performing other circuit functions, it is desirable that the incremental pin count of the additional function be at a minimum. It is also desirable that the partitioning be consistent with the costs of integrating components, which permits the addition of resistances (in a certain range) or active devices at small incremental costs, while generally prohibiting the integration of inductors or capacitors. Thus, the partitioning must preferably take place at a circuit boundary where only nonintegratable components are off the chip and only integratable components are on the chip, and as noted earlier, the interconnections between on and off the chip portions are at a minimum.
The electrical properties of the oscillator are dictated by the application. The present application is to the erase head of a tape recorder. In this application, it is desirable that the voltage swing of the oscillator be optimum, consistent with a limited dc bias, often present in low cost IC designs. There should be a control of the peak current swing, an adequate current drive capability, and efficient dc to ac current conversion.